BACKGROUND

What is allergy?

Allergy refers to the body’s immune system creating an exaggerated response to bodily contact with a foreign protein substance (allergens). This exaggerated response is also called hypersensitivity. Non-allergic people do not respond to allergens because they are harmless . On the other hand, an allergic person, also refered to as atopic person, may respond to an allergen in a variety of ways, such as by coughing, sneezing, itching, having nasal congestion, or wheezing . The most common diagnostic methods for allergies are a skin prick test or a blood test known as RAST (radio-allergosorbent test). A skin prick test is performed by dropping different solutions of allergen proteins into the skin and looking for a reaction. An allergy is identified when a raised wheal with a red surrounding flare occurs at a particular prick location. The RAST blood test accurately measures the amount of the allergy antibody (IgE) in your blood that is fighting against specific allergens . Allergy has no cure but can be maintained by appropriate prevention and treatment. Allergies have been thought to have a genetic component seen mainly in the prevalence of children whose parents have allergies, but no definitive causes of allergy have been identified .

Source: health.yahoo.com

Who has allergies?

Since the 1980’s, allergy prevalence has been increasing across all age, sex, and racial groups. Currently, 50 million, 1 in 5, Americans have allergic conditions. Allergy affects both children and adults, but is more common in children under 18 years of age. Allergy is the 5th leading chronic disease among all Americans, but is the 3rd leading chronic disease among children in America . It has been reported that allergies limit the activity of 40% of children with allergies .

The prevalence of allergy worldwide varies from country to country. Some countries have an allergy prevalence as low as 1% of the population, while other countries have a prevalence as high as 40% of their population. Although it has not been well established, a relationship between allergy and the affluence and lifestyle of a country has been seen .

Why is Allergy important?

In the United States alone, approximately $7 billion is spent each year for allergy medications and office visits. In addition to being costly, allergies contribute to high levels of morbidity and loss of productivity in everyday life. It has been estimated that the annual cost of lost productivity due to allergies is $700 million .

Source: best-prices-pharm-store.com/allergies/about/

How Does the Immune System Affect Allergy?

To fundamentally understand the biological process of allergies, you must first understand a few basic concepts about the immune system. If a harmful foreign object, such as a virus or parasite for instance, is found inside the human body, there are mechanisms in place that destroy the pathogen, protecting us from disease. One of the more notable features of the immune system is its ability to distinguish these harmful pathogens from the human cells, tissues, and other harmless objects. In essence, allergies are derived from an overactive immune system that fights back against pathogens that are completely harmless, such as pollens, insects, or food.

Two key components of the immune system that are involved in responses to both parasites and allergies are lymphocytes (white blood cells) called T cells, and antibodies (immunoglobulins) IgG and IgE. Immunoglobulin is a protein that is used by the immune system to identify the antigen - a specific target, of a foreign object. The most common antibody is immunoglobulin G (IgG), which is found free floating in the plasma. IgG makes up 80% of the antibodies, and provides the majority of immunity against pathogens in the blood stream. IgE on the other hand, is an antibody secreted by the skin and respiratory tracts in response to pathogens invading the skin and airway . IgE is often the pivotal defense against parasites but is also the same antibody that causes an allergic response . When IgE attaches to an antigen, there is a histamine release that can cause swelling or irritation, which are often symptoms of an allergic reaction .

Source: www.ksat.com/encyclopedia/6867416/detail.html

Lymphocytes are also key mechansisms of the body’s defense, acting once the pathogen reaches the blood stream. T cells are white blood cells with a receptor on their surface that helps them identify pathogens, and are involved in the immune response on a cellular level. One type of T cell is the Helper T cell, which recognizes a pathogen, and then sends out chemical signals that activate even more cells to help fight the object. There are two classes of T helper cells, Th1 and Th2, which respond to different pathogens and infections. T helper cells are used to fight both infections and parasites .

Hypotheses About the Increase in Allergy

In recent decades developed countries have experienced a significant rise in the prevalence of allergies. Because allergies and the immune system are so closely intertwined, it is thought that this increase in allergy prevalence has is related to the development or function of our immune system. In 1989, David Strachan, of the London School of Hygiene and Tropical Medicine, developed the “Hygiene Hypothesis,” linking hygiene during development to an increase in allergies later in life. He hypothesized that hygiene leads to more allergies after noticing that large families were less likely to get hay fever than smaller families. He then concluded that this was because the immune system has been ‘trained’ to be tolerant of foreign pathogens. In the Hygiene Hypothesis, T-helper cells (Th1) need to be primed or trained by microorganisms during development, or else Th2 cells will overreact, attacking microorganisms that may not be harmful, such as many common allergens . Essentially, the Hygiene Hypothesis states that the two kinds of T-helper cells, Th1 and Th2, must be in balance for proper immune system function. A lack of microorganisms during development leads to a decrease in Th1 and an increase in Th2, causing more Th2 related reactions such as allergies.

Source: www.immune.org.nz

This hypothesis was revised once researchers realized that there was also a simultaneous increase in autoimmune disorders, which is due to increased Th1 cells. Although the body does need a balance of Th1 and Th2 cells, the determining factor is the balance of T cell regulators and T cell effectors. Regulatory T cells control helper T cells, keeping them from attacking the body’s own tissues, cells, and harmless microorganisms, while effector T cells promote helper T cell immune response .

Using this information, Dr. Graham Rook updated the Hygiene Hypothesis and developed the “Old Friends Hypothesis.” He confirmed these new findings after noticing that the elimination of the pinworm from the United Kingdom coincided with the huge increase in allergy prevalence . The Old Friends hypothesis most generally states that humans need organisms such as intestinal parasites and mycobacteria, not simply allergens, to drive the development of T regulator cells. Currently in developed countries there is very little exposure to intestinal helminthes during development, and one could say that we are missing our ‘old friends.’ The presence of these relatively harmless microorganisms such as parasites and mycobacteria during development teach the immune system to be less sensitive and not to react to every invading pathogen, which thus lowers the incidence of allergy and autoimmune disease.

Source: Yazdanbakhsh, Maria, Peter G. Kremsner, and Ronald Van Ree. "Allergy, Parasites, and the Hygiene Hypothesis." Science. 296 (2002): 490-494.


"Allergy (Allergies) Symptoms, Causes, and Signs." 12 Apr. 2007. MedicineNet.com. 17 May 2007 <http://www.medicinenet.com/allergy/article.htm>.

"Allergy Facts and Figures." Asthma and Allergy Foundation of America. 17 May 2007 <http://www.whatsmyige.com/display.cfm?id=9?sub=30>.

"Overview of Allergy, Its Diagnosis, and Treatment." Allergic Diseases Resource Center. 30 Mar. 2005. World Allergy Organization. 17 May 2007 <<http://www.worldallergy.org/public/allergic_diseases_center/overview.shtml>http://www.worldallergy.org/public/allergic_diseases_center/overview.shtml>.

"Allergy Facts and Figures." Asthma and Allergy Foundation of America. 17 May 2007 <http://www.whatsmyige.com/display.cfm?id=9?sub=30>.

ibid

"Overview of Allergy, Its Diagnosis, and Treatment." Allergic Diseases Resource Center. 30 Mar. 2005. World Allergy Organization. 17 May 2007 <<http://www.worldallergy.org/public/allergic_diseases_center/overview.shtml>http://www.worldallergy.org/public/allergic_diseases_center/overview.shtml>.

ibid

ibid

Purves, William K., David Sadava, Gordon H. Orians, and H C. Heller. Life: the Science of Biology. 7th ed. Sinauer Associates, 2004. 364-386.

Rangaraj S, Doull I. “Hormones not hygiene? Birth order and atopy.” Journal of Clinical and Experimental Allergy. 2003. 33. 277-278.

Purves, William K., David Sadava, Gordon H. Orians, and H C. Heller. Life: the Science of Biology. 7th ed. Sinauer Associates, 2004. 364-386.

Ibid

Hadley, Caroline. “Should auld acquaintance be forgot…” European

Molecular Biology Organization. 2004. Vol 5. No 12.

Rook, Graham and Brunet, Rosa. “Old Friends for breakfast” Journal of

Clinical and Experimental Allergy. 2005. 35. 841-842.

Hadley, Caroline. “Should auld acquaintance be forgot…” European

Molecular Biology Organization. 2004. Vol 5. No 12.

Rook, Graham and Brunet, Rosa. “Old Friends for breakfast” Journal of

Clinical and Experimental Allergy. 2005. 35. 841-842.

 


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